This invention relates to a head-mounted device for positioning a pair of breathing circuit tubes and a gas sensor.
Capnography is the monitoring of a patient's airway and more specifically, of end-tidal carbon dioxide (CO.sub.2) concentration. It is rapidly emerging as the standard procedure for monitoring the adequacy of a patient's ventilation during the administration of anesthetic gases. Capnography is a more reliable indicator of patient ventilation than any qualitative clinical sign, such as chest excursion, observation of a reservoir breathing bag, or auscultation of breathing sounds.
A CO.sub.2 capnometer monitors the amount of carbon dioxide gas exhaled by a patient. Carbon dioxide is made in the patient's tissues and is carried by the circulatory system to the lungs. There, it is carried away in alveolar ventilation, mixes with dead space ventilation, and is exhaled. Thus, the output of a capnometer--a capnograph--describes four CO.sub.2 related activities: metabolic production; circulation; alveolar ventilation; and dead space ventilation.
A typical CO.sub.2 capnograph is shown in FIG. 1A. The graph is a plot of CO.sub.2 concentration on the vertical axis and time on the horizontal axis. In a normal patient, inspired carbon dioxide should always be zero. At the beginning of exhalation, the patient's airway carbon dioxide steadily rises toward a relatively flat plateau. After exhalation is completed, carbon dioxide again decreases toward zero.
The CO.sub.2 capnometer determines carbon dioxide concentration via infrared absorption at a specific wavelength. The equipment includes a sensor positionable in the breathing circuit. The sensor is connected to a monitor which can be positioned off to the side, away from the patient. In contrast, the sensor needs to be as close as possible to the patient's nose or mouth and integrated with the breathing circuit tubes. The size of the sensor (about the size of a cigarette box), its weight (about 5 lbs.), and the fact that it generates heat (up to about 106.degree. F.), creates problems in positioning the sensor near the patient's face. This is particularly significant during maxillofacial surgery, such as head, neck, oral, or plastic surgery, where it is necessary to leave the neck and face unobstructed so that the surgeon can perform the operation. Not only is it important to keep the face and neck areas clear, but it is important to position the sensor and breathing tubes so that they do not cause the patient irritation and so that they are not easily disconnected or kinked, which would interfere with their operation.
It is an object of this invention to provide an apparatus for supporting a sensor for a breathing circuit.
Another object is to provide a headband mounting device for supporting a sensor and breathing circuit tubes adjacent the centerline of the forehead and up over the head, thereby leaving the face and neck areas clear.
Yet another object is to provide such a device which causes minimum irritation to the patient and prevents dislodgement and kinking of the sensor or tubes.
A further object is to provide such a device which protects the patient from heat generated by a sensor.